Wide varieties of semiconductor memory devices have been developed and continuously employed in new and expanded uses. The newly developed uses require increased capabilities of integrated circuits but decreased cost in manufacturing. Many semiconductor devices are comprised of multiple types of circuits such as memory and logic circuits. Flash memory has become increasingly popular in recent years. Flash memory cells are typically formed, along with other circuits (non-memory circuits) such as core circuits, as embedded flash memory.
A typical flash memory includes a memory array having a large number of memory cells arranged in blocks. Each of the flash memory cells is fabricated as a field-effect transistor having a control-gate and a floating-gate. The floating-gate is capable of holding charges and is separated from source and drain regions contained in a substrate by a layer of thin oxide. The memory cells may be capable of several operations including program, read, write, and erase. For example, memory cells may be electrically charged by injecting electrons from the drain region through the oxide layer onto the floating-gate. The charges may be removed from the floating-gate, in one known approach, by tunneling the electrons to the source through the oxide layer during an erase operation. The data in a memory cell is thus determined by the presence or absence of a charge on the floating-gate.
While the sizes of semiconductor memory devices become smaller, elements of the layout, for example, bit lines, word lines, control gate lines and erase gate lines are formed finer and closer. However, the closer distance between the elements can induce some defects and affect the efficiency of semiconductor memory devices.